The present invention relates to a method and an apparatus of generating an indium ion beam from an ion source, which is applied to, such as an ion beam irradiating apparatus as an ion implantation apparatus. The present invention especially relates to a method and an apparatus of generating an indium ion beam in a stable amount.
The indium ion has been noticeable in a technical field of production of semi-conductors. Japanese Patent Unexamined Publication No. Hei 03-13576 describes a method of generating an indium ion beam from an ion source, comprising the steps of pre-annealing a heating furnace (carbon container) including an indium iodide therein at temperature in the range of 100 to 200xc2x0 C., increasing the temperature of the heating furnace at 300 to 500xc2x0 C. to vaporize the indium iodide, introducing the steam of the indium iodide vaporized the indium iodide into a plasma generator (discharging chamber) to ionize it therein by an arc discharge and thus generates plasma, and deriving an indium ion beam from this plasma.
But, in this method, since a melting point of the indium iodide is at 210xc2x0 C., if the heating furnace is operated at 300 to 500xc2x0 C. as mentioned, the indium iodide is completely melted into a liquid. As a result, the heating furnace, the plasma generator, and further a steam introducing pipe between both and the like are adhered with the liquidized indium iodide being like mucus. Therefore, the inside of the heating furnace, the plasma generator, and the steam introducing pipe are smudged by the liquidized indium iodide being like mucus. The steam pipe is clogging, so that the indium ion beam cannot be taken out stably.
Besides, owing to smudging, the heating furnace, the plasma generator, and the steam introducing pipe must be cleaned or exchanged frequently. For example, each time when the operation of the ion source is stopped, the heating furnace, the plasma generator, and the steam introducing pipe must be cleaned or exchanged. This is practically intolerable.
On the other hand, an inventor of this invention find the following steps for generating the indium ion beam, while avoiding the pipe from adhering the liquidized indium trifluoride and avoiding the heating furnace, the plasma generator, and the steam introducing pipe therebetween from smudging and clogging.
A first step is pre-annealing of the indium trifluoride at 250 to 450xc2x0 C. for removing water content. The indium trifluoride as a solid material is introduced at the heating furnace. A second step is to increase the temperature of the heating furnace from 450xc2x0 C. to lower than 1170xc2x0 C. of the melting point of the indium trifluoride for vaporization of the indium trifluoride. A third step is to introduce the steam of the indium trifluoride into. a plasma generator. A forth step is ionizing the steam of the indium trifluoride by an arc discharge to generate a plasma. A fifth step is deriving the indium ion beam from the plasma.
But, it was found that there still remained rooms as mentioned below for improving the above mentioned method employing the indium trifluoride as the solid material.
The vapor pressure of the indium trifluoride becomes very high by presence of water content. When the water content contained in the indium trifluoride is much, the steam amount of the indium trifluoride becomes more. Therefore, the amount of the indium ion is much, since the ionized steam amount of the indium trifluoride is increasing.
When the temperature of the heating furnace is constant, the steam amount of the indium trifluoride goes down in a short time together with lost of the water content contained in the indium trifluoride. Therefore, the amount of the indium ion beam generated from the ion source also goes down. For example, the amount of the indium ion beam decreases 20% to 70% of an initial amount (i.e., at starting time) in an hour after starting the generation thereof.
One example is shown in FIG. 2 as a comparative example. FIG. 2 shows changes in the amount of the indium ion beam accompanying with passing time from generating the indium ion beam, when the temperature of the heating furnace was maintained constant. The amount of the indium ion beam rapidly goes down until about 30% of the initial amount in one hour after the indium ion beam starts to generate in the comparative example. In the comparative example an indium trifluoride anhydride is used as the solid material, and the pre-annealing is performed at 450xc2x0 C. for one hour.
Such rapid decrease in the amount of the indium ion beam is not preferable. For example, this makes difficult in the ion source to control the amount of the indium ion beam generated therefrom and control an implantation amount of the indium ion, when the indium ion beam is applied to the ion implantation.
More specifically, the amount of the indium ion beam rapidly goes down, even if the temperature of the heating furnace for compensation for decreasing the amount of the indium ion beam is increasing, the amount of the indium ion beam again rapidly goes down. Such repetition goes on and the amount of the indium ion beam is not stabilized indefinitely. For instance, it takes 3 to 4 days for stabilizing the amount of the indium ion beam. It is not practical use.
For using the indium trifluoride, in spite of pre-annealing at 250 to 450xc2x0 C. to remove the water content, the problem as mentioned above has been present.
For using a substance called as an indium trifluoride anhydride, which contains no water, the similar tendency has existed as mentioned.
It is an object of the invention to provide an apparatus and a method enabling to generate the indium ion beam in a stable amount.
As one of methods of generating the indium ion beam according to the invention, a method of generating an indium ion beam comprises steps of annealing a solid material including an indium compound in a heating furnace to generate a steam therefrom, and ionizing the steam supplied from the heating furnace in a plasma generator for ionizing the steam supplied from the heating furnace to generate plasma. In this method it is characterized by using an indium trifluoride as said solid material which is pre-annealed at a temperature in the range of 600xc2x0 C. to lower than 1170xc2x0 C. in the furnace.
The invention is included as mentioned above, and has the following effects.
It is possible to remove unstable factors in the vaporizing amount of the solid material included the indium compound so that the indium ion beam can be generated in the stable amount. As a result, the control of the amount of the indium ion beam and the control of the amount of implanting the indium ion using the indium ion beam are very easy.
Passing through various investigations, it is found that the water content contained in the indium trifluoride being the solid material has two types. First is water content merely adhered to the molecule of the indium trifluoride (InF3). This can easily be vaporized by pre-annealing at 250 to 450xc2x0 C. Only this water content has been studied, so that it has been satisfied with the removal of the water content.
However, it has been found a second of the water content is exited. This is the water content combined with a molecule of the indium trifluoride (InF3) through a molecular combination, namely, the water content of the molecular combination of a formation of InF3xe2x88x92x (H2O). x is 1, 2 or 3, and typically 3.
The water content remains after the indium ion beam starts to generate, since the water content of this molecular combination could not be removed by the conventional pre-annealing temperature. Therefore, the water content slowly goes down. It makes unstable the amount of vaporizing the indium trifluoride.
A substance called as the indium trifluoride. anhydride absorbs the water, if it is exposed to an atmospheric air even a little. Since the portion of the water combines with the molecule of the indium trifluoride via molecule combination, it cannot be easily removed.
On the other hand, it has been found that if once pre-annealing the indium trifluoride as the solid matters at 600xc2x0 C. or higher, the following chemical reaction was rapidly accelerated.
InF3xe2x88x92x(H2O)+heatxe2x86x92In(OF)xF3xe2x88x92x+xH2xe2x80x83xe2x80x83[Formula 1]
x=1, 2 or 3.
By the reaction, it is possible to rapidly dissolve the water content (H2O in the left side of the formula) molecule-combined as an unstable factor in the amount of vaporizing the indium trifluoride. xe2x80x9cIn(OF)xF3xe2x88x92xxe2x80x9d in the right side has oxygen but contains no water.
When the indium trifluoride is heated once, the indium trifluoride changed into In(OF)xF3xe2x88x92x contains no water. Therefore, the vaporizing amount of the indium trifluoride by annealing is stable. It keeps the indium ion beam generating in the stable amount by annealing In(OF)xF3xe2x88x92x as the solid material in the heating furnace. In other words, the time rate of change in the amount of the indium ion beam respect to a passing time from gegenerating the indium ion beam can be made smaller considerably than in comparison with the related art. The results are shown in FIG. 2 and will be referred to later.
If the annealing temperature of the indium trifluoride is less than 600xc2x0 C., the reaction of the formula 1 scarcely appears and an effect cannot be obtained.
If the annealing temperature of the indium trifluoride is 1170xc2x0 C. of the melting point of the indium trifluoride or higher, the indium trifluoride is melted to smudge or clog the heating furnace, the plasma generator and the steam pipe therebetween.
However, if increasing the annealing temperature too high, the effect of causing the reaction of the formula 1 is not changed so much. Accordingly, the pre-annealing temperature of the indium trifluoride is preferably from 600 to 700xc2x0 C. in the above range, and this temperature range is most practical.
The pre-annealing time of the indium trifluoride depends on annealing temperature. If the annealing temperature is in the range of 600 to 700xc2x0 C., around 30 to 90 minutes are desirable for the pre-annealing time. It is insufficient to take less than 30 minutes for the pre-annealing time to uniformly heat the whole of the indium trifluoride as the solid material. But if it takes more than 90 minutes, the annealing effect is hardly available and uselessness of time is much. Thus, around one hour is more desirable for the pre-annealing time of the indium trifluoride.
Incidentally, there may be installed a control device for controlling the pre-annealing temperature of the indium trifluoride in the heating furnace, so that the temperature in the heating furnace keeps in the range of 600xc2x0 C. to less than 1170xc2x0 C. prior to properly generating the indium ion beam prior to generating the indium ion beam of an predetermined amount. In such a manner, the operation of the ion source may be curtailed otherwise automatized.
In accordance with the above invention, It is possible to remove unstable factors in the vaporizing amount of the solid material included the indium compound so that the indium ion beam can be generated in the stable amount. As a result, the control of the amount of the indium ion beam and the control of the amount of implanting the indium ion using the indium ion beam are very easy, while the ion source can be curtailed or automatized.
Further, as In(OF)xF3xe2x88x92x is made by the pre-annealing as mentioned above, in substitution for the indium trifluoride, In(OF)xF3xe2x88x92x (x=1, 2 or 3) may be employed as the solid material to be supplied to the heating furnace, and also in this case a same effect is obtained. Namely, the indium ion beam can be generated in the stable amount.
The invention is included as mentioned above, and has the following effects.
It is possible to remove unstable factors in the vaporizing amount of the solid material included the indium compound so that the indium ion beam can be generated in the stable amount. As a result, the control of the amount of the indium ion beam and the control of the amount of implanting the indium ion using the indium ion beam are very easy.